Client on iPhone does not connect (iOS 10, webdav)

Please help us by providing the following info.

Steps to reproduce
Enter server url in the client

Expected behaviour
Connect to the server (webdav)

Actual behaviour
Errormessage: Server not found (Server nicht gefunden)

Mobile client configuration
ownCloud client version 3.5.1 on iOS 10.1

Server configuration
Operating system: Debian 8
Web server: Apache 2.4
Database: MySQL 5.?
PHP version: 7.0
ownCloud version (see ownCloud admin page): 9.0.2
Updated from an older ownCloud or fresh install: Updated from 9.0.1 to 9.0.2
ownCloud log (data/owncloud.log): last entry from 2016-10-13, nothing that is related to this error, no errors due to update/upgrade

Special configurations (external storage, external authentication, reverse proxy, server-side-encryption):
No external storage, no external authentification, no proxy...

Windows, (any) Android and Linux client are working fine, only on iOS 10.x (can't try with older os version) it does not work. On Safari browser it works too.
It is connected to server with TLSv1.2 and a Let's Crypt certificate. But it works with all other clients on any other OS (can't try on mac, i don't have one), so i don't think it is an incorrect configuration of the server...

I don't know how to solve this problem.


(sorry if there are some gramatically erros, i'm a german guy with only "low" english skills.. but often i'm more lucky when i ask a question in english...)

It probably won't solve your issue here but please always use a recent version of oC before posting any issues. In the 9.0.x branch this is 9.0.5:

Also closing as a duplicate of the following thread which might be exactly the same issue: